Utilizing of brush stroking techniques in the generation of computer images

ABSTRACT

A form of &#34;brushing&#34; an computer graphic image is disclosed. The method includes brushing a simulated brush stroke along a path in a computer graphics image by converting the path to a series of corresponding line segments; determining a current convex brush edge of the path; determining a series of substantially equally spaced points along the convex edge; determining corresponding parametric points along the path; and utilising the parametric points to place brush template structures in the computer graphics image. In a first refinement, the opacity channel is combined such that the maximum of a current brush template opacity value and a current computer graphic image opacity channel value becomes the new current computer graphic image opacity channel value. In a second refinement, the opacity channel is combined such that the minimum of a current brush template opacity value and a current computer graphic image opacity channel value becomes the new current computer graphic image opacity channel value. In a third refinement, the computer graphic image further comprises a footprint channel which is set when each pixel is composited and the opacity channel is only composited with the computer graphic image opacity channel when the footprint channel is not set.

CROSS REFERENCES TO RELATED APPLICATIONS

The following co-pending US patent applications, identified by their US patent application serial numbers (USSN), were filed simultaneously to the present application on July 10, 1998, and are hereby incorporated by cross-reference:

09/113,060; 09/113,070; 09/113,073; 09/112,748; 09/112,747; 09/112,776; 09/112,750; 09/112,746; 09/112,743; 09/112,742; 09/112,741; 09/112,740; 09/112,739; 09/113,053; 09/112,738; 09/113,067; 09/113,063; 09/113,069; 09/112,744; 09/113,058; 09/112,777; 09/113,224; 09/112,804; 09/112,805; 09/113,072; 09/112,785; 09/112,797; 09/112,796; 09/113,071; 09/112,824; 09/113,090; 09/112,823; 09/113,222; 09/112,786; 09/113,051; 09/112,782; 09/113,056; 09/113,059; 09/113,091; 09/112,753; 09/113,055; 09/113,057; 09/113,054; 09/112,752; 09/112,759; 09/112,757; 09/112,758; 09/113,107; 09/112,829; 09/112,792; 09/112,791; 09/112,790; 09/112,789; 09/112,788; 09/112,795; 09/112,749; 09/112,784; 09/112,783; 09/112,763; 09/112,762; 09/112,737; 09/112,761; 09/113,223; 09/112,781; 09/113,052; 09/112,834; 09/113,103; 09/113,101; 09/112,751; 09/112,787; 09/112,802; 09/112,803; 09/113,097; 09/113,099; 09/113,084; 09/113,066; 09/112,778; 09/112,779; 09/113,077; 09/113,061; 09/112,818; 09/112,816; 09/112,772; 09/112,819; 09/112,815; 09/113,096; 09/113,068; 09/113,095; 09/112,808; 09/112,809; 09/112,780; 09/113,083; 09/113,121; 09/113,122; 09/112,793; 09/112,794; 09/113,128; 09/113,127; 09/112,756; 09/112,755; 09/112,754; 09/112,811; 09/112,812; 09/112,813; 09/112,814; 09/112,764; 09/112,765; 09/112,767; 09/112,768; 09/112,807; 09/112,806; 09/112,820; 09/112,821; 09/112,822; 09/112,825; 09/112,826; 09/112,827; 09/112,828; 09/113,111; 09/113,108; 09/113,109; 09/113,123; 09/113,114; 09/113,115; 09/113,129; 09/113,124; 09/113,125; 09/113,126; 09/113,119; 09/113,120; 09/113,221; 09/113,116; 09/113,118; 09/113,117; 09/113,113; 09/113,130; 09/113,110; 09/113,112; 09/113,087; 09/113,074; 09/113,089; 09/113,088; 09/112,771; 09/112,769; 09/112,770; 09/112,817; 09/113,076; 09/112,798; 09/112,801; 09/112,800; 09/112,799; 09/113,098; 09/112,833; 09/112,832; 09/112,831; 09/112,830; 09/112,836; 09/112,835; 09/113,102; 09/113,106; 09/113,105; 09/113,104; 09/112,810; 09/112,766; 09/113,085; 09/113,086; 09/113,094; 09/112,760; 09/112,773; 09/112,774; 09/112,775; 09/112,745; 09/113,092; 09/113,100; 09/113,093; 09/113,062; 09/113,064; 09/113,082; 09/113,081; 09/113,080; 09/113,079; 09/113,065; 09/113,078; 09/113,075.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to digital image processing and in particular discloses The Utilising of Brush Stroking Techniques in the Generation of Computer Images.

Further the present invention relates to the creation of digital images and in particular relates to brush stroking techniques utilised in the creation of digital images.

BACKGROUND OF THE INVENTION

Packages, such as Adobe's Photoshop (Trade Mark) allow for the creation of complex images through the manipulation of many different parts or structures in an image to produce a final overall image. In particular, these packages normally provide for complex paint brushing techniques or filters. The implementation details of these paint brushing techniques being well known and being set out in the standard computer graphics texts. Familiarity with such techniques is hereinafter assumed.

Known techniques include utilising a paint brush having a predetermined degree of transparency or, in the alternative, opacity. In particular, the utilisation of brushing techniques to achieve water color like effects are provided within the aforementioned package. Unfortunately, when utilising such brushing techniques, often imperfections are produced particularly when a paint brush rounds tight comers or loops on itself. Additionally, there is general need for effective and efficient brushing techniques in the field of computer graphics.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide for alternative forms of brushing so as to produce useful effects.

In accordance with the first aspect of the present invention there is provided a method of brushing a simulated brush stroke along a path in a computer graphics image the method comprising the steps of converting the path to a series of corresponding line segments; determining a current convex brush edge of said path; determining a series of substantially equally spaced points along said convex edge; determining corresponding parametric points along the path; and utilising the parametric points to place brush template structures in said computer graphics image.

In a first refinement, the opacity channel is combined such that the maximum of a current brush template opacity value and a current computer graphic image opacity channel value becomes the new current computer graphic image opacity channel value. In a second refinement, the opacity channel is combined such that the minimum of a current brush template opacity value and a current computer graphic image opacity channel value becomes the new current computer graphic image opacity channel value. In a third refinement, the computer graphic image further comprises a footprint channel which is set when each pixel is composited and said opacity channel is only composited with the computer graphic image opacity channel when said footprint channel is not set.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 illustrates a flow chart of the steps in the preferred embodiment in compositing brush strokes;

FIG. 2 illustrates the process conversion of Bezier curves to piecewise line segments;

FIG. 3 illustrates the brush stroking process; and

FIG. 4 illustrates suitable brush stamps for use by the preferred embodiment.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

Turning now to FIG. 1, there is illustrated the steps of the preferred embodiment. It is assumed that the brush stroke is defined as a piecewise Bezier curve as is standard practice. The brush stroke is further assumed to have a predetermined thickness. The stroke is made up of a series of Bezier curves. The first step 11 is to process each piecewise Bezier curve. Each Bezier curve is first converted to a corresponding piecewise linear curve 12 utilising standard techniques. Next, the "fastest" edge, whose meaning will become more apparent hereinafter, is utilised to "step along" the fastest edge in predetermine increments. The positions are utilised to composite brush strokes 14.

Turning now to FIG. 2, there is illustrated a first Bezier curve 20 which forms the basis of brush stroke 21. The process of converting the Bezier curve 20 to a corresponding series of line segments eg. 22. The process of linearisation into piecewise linear segments is standard and well known, being covered in the usual texts. As part of the linearisation process, the normals eg. 24 at each of the line end points are also determined. The normals can be determined from the lines adjoining a point eg. 25 by means of interpolation between the line gradients if necessary.

Turning now to FIG. 3, there is shown an enlarged view of two line segments eg. 30, 31. For each point eg. 32 the normals eg. 33, 34 are projected out on each side to a distance of the brush stroking width. The point 36 having projected normals 37, 38. Next, the distance 39 is measured between normals 33, 37 and the distance 40 is measured between the normal 34, 38. A "fastest" edge is defined to be the side having the greatest distance in the sense that a body travelling along the edge 39 would have to travel substantially faster than along the edge 40. Hence, the fastest edge will be the convex edge of a curve.

The fastest edge is utilised to define a predetermined number of points which are parametrically spaced apart by equal amounts. The example of FIG. 3 showing three points eg. 43-45 which defined equally spaced intervals "in distance" along the line 39. The number of intervals being substantially greater than that illustrated in FIG. 3.

Next, a corresponding parametric position of each of the points is determined and is utilised to determine corresponding parametric points along the line 30. The corresponding locations being positions where brush strokes are to be placed.

Turning now to FIG. 4, there is illustrated a series of brush stamps 46, 47, 48. The two stamps 46, 48 being utilised for the end portions of a line and the portion 47 being continually utilised along the middle portion of a line.

The brush stamp is defined by three separate channels being a matte channel, a bump map channel and a footprint channel. The in the particular example of FIG. 4, the matte channel of the brush is illustrated. In the first technique, known as the "max" technique the matte and bump map channel are utilised to build a brush stroke in a separate brushing buffer. In this compositing technique, a brush is built up by taking the maximum opacity ie, the opacity is replaced with a new opacity when the new opacity exceeds the old opacity presently in the buffer. The results produced are similar to the Photoshop air brushing or painting.

In a second compositing technique, hereinafter known as the "footprint" technique. The footprint channel is utilised such that the matte value is changed only if a previous brush stamp for a current line has not written to the brush buffer for that pixel. In the third technique, again the matte and the bump map channel are utilised but this time the minimum of the matte channel and the background, provided the minimum is below an absolute minimum is utilised.

The above techniques were found to give good results, especially in the simulation of water color effects.

The following code segment illustrates the line following process of the preferred embodiment:

    ______________________________________                                         /*                                                                              * $RCSfile: G2PolylineNav2.h$                                                  *                                                                              * G2.sub.-- PolylineNavigator2 template class definition.                      *                                                                              * Author: Paul Lapstun, 1996/11/7                                              * Copyright Silverbrook Research 1996.                                         *                                                                              * $Log$                                                                        */                                                                            #ifndef .sub.-- G2PolylineNav2.sub.-- h.sub.--                                 #define .sub.-- G2PolylineNav2.sub.-- h.sub.--                                 #include <bool.h>                                                              #include <G2Polyline.h>                                                        #include <G2VectorList.h>                                                      template<class T>                                                              class G2.sub.-- PolylineNavigator2                                             public:                                                                                     G2.sub.-- PolylineNavigator2(G2.sub.-- Polyline<T>                const& p1, G2.sub.-- VectorList<T> const& t1, G2.sub.-- Real halfWidth)                        : m.sub.-- polyline(p1), m.sub.-- tanList(t1),                 m.sub.-- halfWidth(halfWidth) { Start ( ); }                                   bool           AtEnd( ) const { return m.sub.-- pi ==                          m.sub.-- polyline.end( ); }                                                    bool           Empty( ) const { return                                         m.sub.-- polyline.empty( ): }                                                  void           Start( );                                                       void           Advance(T s);                                                   G2.sub.-- Point<T>                                                                            Point( ) const;                                                 G2.sub.-- Vector<T>                                                                        Tangent( ) const;                                                  private:                                                                       void           SetEffectiveSegmentLength( );                                   private:                                                                       G2.sub.-- Polyline<T> const&  m.sub.-- polyline;                                                     // polyline being                                                              navigated                                                G2.sub.-- VectorList<T> const& m.sub.-- tanList;                                                     // tangent list being                                                          navigated                                                G2.sub.-- Real    m.sub.-- halfWidth;// half `brush` width                     G2.sub.-- Polyline<T>::const.sub.-- iterator                                                m.sub.-- pi;                                                                          // polyline iterator                                       G2.sub.-- VectorList<T>::const.sub.-- iterator                                              m.sub.-- ti;                                                                          // tangent list iterator                                   G2.sub.-- Point<T>                                                                            m.sub.-- p0;                                                                            // point at atart of                                   segment                                                                        G2.sub.-- point<T>                                                                            m.sub.-- p1;                                                                            // point at end of segment                             G2.sub.-- Vector<T>                                                                        m.sub.-- v0;                                                                             // tangent at start of segment                           G2.sub.-- Vector<T>                                                                        m.sub.-- v1;                                                                             // tangent at end of segment                             G2.sub.-- Vector<T>                                                                        m.sub.-- n0;                                                                             // normal at start of segment                            G2.sub.-- Vector<T>                                                                        m.sub.-- n1;                                                                             // normal at end of segment                              T                 m.sub.-- length;                                                                        // length of current                                segment                                                                        T                 m.sub.-- s;                                                                             // displacement along                               current segment                                                                G2.sub.-- Real    m.sub.-- t;                                                                             // parameter along                                  current segment                                                                };                                                                             template<class T>                                                              inline                                                                         void                                                                           G2.sub.-- PolylineNavigator2<T>::Start( )                                      {                                                                              // set iterators to beginning                                                  m.sub.-- pi = m.sub.-- polyline.begin( );                                      m.sub.-- ti = m.sub.-- tanList.begin( );                                       if (AtEnd( ))                                                                  return; // empty . . .                                                         // get segment start point and tangent                                         m.sub.-- p0 = *m.sub.-- pi++;                                                  m.sub.-- v0 = *m.sub.-- ti++;                                                  m.sub.-- n0 = m.sub.-- v0.Normal( ).Normalise( ) * m.sub.-- halfWidth;         if (AtEnd( ))                                                                  return; // shouldn't happen . . .                                              // get segment end point and tangent                                           m.sub.-- p1 = *m.sub.-- pi;                                                    m.sub.-- v1 = *m.sub.-- ti;                                                    m.sub.-- n1 = m.sub.-- v1.Normal( ).Normalise( ) * m.sub.-- halfWidth;         // set effective segment length                                                SetEffectiveSegmentLength( );                                                  // reset displacement and parameter at start                                   m.sub.-- s = 0;                                                                m.sub.-- t = 0;                                                                }                                                                              template<class T>                                                              inline                                                                         void                                                                           G2.sub.-- PolylineNavigator2<T>::Advance(T s)                                  {                                                                              if (AtEnd( ))                                                                  return;                                                                        // skip segments until s falls in current segment                              while ((m.sub.-- s + s) > m.sub.-- length)                                     {                                                                              // get segment start point and tangent                                         m.sub.-- p0 = m.sub.-- p1;                                                     m.sub.-- v0 = m.sub.-- v1;                                                     m.sub.-- n0 = m.sub.-- n1;                                                     // get segment end point and tangent                                           m.sub.-- pi++;                                                                 m.sub.-- ti++;                                                                 if (AtEnd( ))                                                                  return; // genuine end . . .                                                   m.sub.-- p1 = *m.sub.-- pi;                                                    m.sub.-- v1 = *m.sub.-- ti;                                                    m.sub.-- n1 = m.sub.-- v1.Normal( ).Normalise( ) * m.sub.-- halfWidth;         // allow for rest of previous segment                                          s -= (m.sub.-- length - m.sub.-- s);                                           // set effective segment length                                                SetEffectiveSegmentLength( );                                                  // reset displacement at start of segment                                      m.sub.-- s = 0;                                                                }                                                                              // move along current segment by remaining s                                   // and compute parameter at new displacement                                   m.sub.-- s += s;                                                               m.sub.-- t = m.sub.-- s / m.sub.-- length;                                     }                                                                              template<class T>                                                              inline                                                                         G2.sub.-- Point<T>                                                             G2.sub.-- PolylineNavigator2<T>::Point( ) const                                {                                                                              if (AtEnd( ))                                                                  return G2.sub.-- Point<T>(0, 0);                                               return m.sub.-- p0.Interpolate(m.sub.-- p1, m.sub.-- t) ;                      }                                                                              template<class T>                                                              inline                                                                         G2.sub.-- Vector<T>                                                            G2.sub.-- PolylineNavigator2<T>::Tangent( ) const                              {                                                                              if (AtEnd( ))                                                                  return G2.sub.-- Vector<T>(0, 0);                                              G2.sub.-- Vector<T> tangent = m.sub.-- v0.Interpolate(m.sub.-- v1,             m.sub.-- t);                                                                   return tangent;                                                                }                                                                              template<class T>                                                              inline                                                                         void                                                                           G2.sub.-- PolylineNavigator2<T>::SetEffectiveSegmentLength( )                  {                                                                              // the normals at the end points of the current line                           // segment have already been computed and scaled in                            // length by half the `brush` width; now construct                             // vectors which join the ends of the normals; these                           // vectors are parallel to the line segment which                              // approximates the curve; the vector on the convex                            // side of the curve is longer than the line segment;                          // the vector on the concave side is shorter; choose                           // the length of the longer vector for displacement                            // stepping; note that a parameter t computed at a                             // particular displacement along the chosen vector                             // can be used directly to compute the point on the                            // line segment which approximates the curve                                   G2.sub.-- Vector<T> vectorA = (m.sub.-- p1 + m.sub.-- n1) - (m.sub.-- p0       + m.sub.-- n0);                                                                G2.sub.-- Vector<T> vectorB = (m.sub.-- p1 - m.sub.-- n1) - (m.sub.-- p0       - m.sub.-- n0);                                                                G2.sub.-- Real len2A = vectorA.LengthSquared( );                               G2.sub.-- Real len2B = vectorB.LengthSquared( );                               if (len2A > len2B)                                                             m.sub.-- length = sqrt(len2A);                                                 else                                                                           m.sub.-- length = sqrt(len2B);                                                 }                                                                              #endif /* .sub.-- G2PolylineNav2.sub.-- h.sub.--  */                           ______________________________________                                    

It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiment without departing from the spirit or scope of the invention as broadly described. The present embodiment is, therefore, to be considered in all respects to be illustrative and not restrictive.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used. However presently popular ink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal ink jet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy-inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal ink jet applications. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per print head, but is a major impediment to the fabrication of pagewidth print heads with 19,200 nozzles.

Ideally, the ink jet technologies used meet the stringent requirements of in-camera digital color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new ink jet technologies have been created. The target features include:

low power (less than 10 Watts)

high resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the ink jet systems described below with differing levels of difficulty. Forty-five different ink jet technologies have been developed by the Assignee to give a wide range of choices for high volume manufacture. These technologies form part of separate applications assigned to the present Assignee as set out in the list under the heading Cross References to Related Applications.

The ink jet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems

For ease of manufacture using standard process equipment, the print head is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the print head is 100 mm long, with a width which depends upon the ink jet type. The smallest print head designed is covered in US Patent Application No. 09/112,764, which is 0.35 mm wide, giving a chip area of 35 square mm. The print heads each contain 19,200 nozzles plus data and control circuitry.

Ink is supplied to the back of the print head by injection molded plastic ink channels. The molding requires 50 micron features, which can be created using a lithographically micromachined insert in a standard injection molding tool. Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The print head is connected to the camera circuitry by tape automated bonding.

Tables of Drop-on-Demand Ink Jets

The present invention is useful in the field of digital printing, in particular, ink jet printing. A number of patent applications in this field were filed simultaneously and incorporated by cross reference.

Eleven important characteristics of the fundamental operation of individual ink jet nozzles have been identified. These characteristics are largely orthogonal, and so can be elucidated as an eleven dimensional matrix. Most of the eleven axes of this matrix include entries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of ink jet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types)

Nozzle clearing method (9 types)

Nozzle plate construction (9 types)

Drop ejection direction (5 types)

Ink type (7 types)

The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of ink jet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain ink jet types have been investigated in detail. Forty-five such inkjet types were filed simultaneously to the present application.

Other ink jet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the forty-five examples can be made into ink jet print heads with characteristics superior to any currently available ink jet technology.

Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The simultaneously filed patent applications by the present applicant are listed by USSN numbers. In some cases, a print technology may be listed more than once in a table, where it shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.

    __________________________________________________________________________     ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS)                        Description           Advantages   Disadvantages     Examples                  __________________________________________________________________________     Thermal                                                                              An electrothermal heater heats the                                                             ♦ Large force generated                                                       ♦ High                                                                             ♦                                                                Canon Bubblejet           bubble                                                                               ink to above boiling point,                                                                    ♦ Simple construction                                                         ♦ Ink carrier limited to                                         water              1979 Endo et al GB             transferring significant heat to the                                                           ♦ No moving parts                                                             ♦ Low efficiency                                                                    patnet 2,007,162               aqueous ink. A bubble nucleates                                                                ♦ Fast operation                                                              ♦ High temperatures                                              required          ♦                                                                Xerox heater-in-pit             and quickly forms, expelling the ink.                                                          ♦ Small chip area required                                                    ♦ High mechanical                                                                   1990 Hawkins et al             The efficiency of the process is low,                                                           for actuator                                                                               ♦ Unusual materials                                              required           U.S. Pat. No.                  with typically less than 0.05% of the                                                                       ♦ Large drive                                                    transistors        4,899,181                      electrical energy being transformed                                                                         ♦ Cavitation causes                                              actuator failure  ♦                                                                Hewlett-Packard                 into kinetic energy of the drop.                                                                            ♦ Kogation reduces                                               bubble formation   TIJ 1982 Vaught et                                          ♦ Large print heads are                                          difficult to       al U.S. Pat. No.                                             fabricate         4,490,728                Piezoelectric                                                                        A piezoelectric crystal such as lead                                                           ♦ Low power consumption                                                       ♦ Very large area                                                required for actuator                                                                            ♦                                                                Kyser et al U.S.                lanthanum zirconate (PZT) is                                                                   ♦ Many ink types can be                                                       ♦ Difficult to integrate                                         with electronics   Pat. No. 3,946,398             electrically activated, and either                                                             ♦ Fast operation                                                              ♦ High voltage drive                                             transistors       ♦                                                                Zoltan U.S. Pat.                expands, shears, or bends to apply                                                             ♦ High efficiency                                                                                No. 3,683,212                  pressure to the ink, ejecting drops.                                                                        ♦ Full pagewidth print                                           heads             ♦ 1973                                                           Stemme U.S.                                                   impractical       Pat. No. 3,747,120                                           due to actuator size                                                                            ♦                                                                Epson Stylus                                                 ♦ Requires electrical                                            poling in high    ♦                                                                Tektronix                                                     field strengths during                                                                          ♦                                                                IJ04                      Electro-                                                                             An electric field is used to activate                                                          ♦ Low power consumption                                                       ♦ Low maximum strain                                             (approx. 0.01%)   ♦                                                                Seiko Epson, Usui         strictive                                                                            electrostriction in relaxor materials                                                          ♦ Many ink types can be                                                       ♦ Large area required                                            for actuator due to                                                                               et al JP 253401/96             such as lead lanthanum zirconate                                                               ♦ Low thermal expansion                                                        low strain       ♦                                                                IJ04                            titanate (PLZT) or lead magnesium                                                              ♦ Electric field strength                                                     ♦ Response speed is                                              marginal (˜10 μs)                        niobate (PMN).   required (approx. 3.5                                                                      ♦ High voltage drive                                             transistors required                                               V/μm) can be generated                                                                  ♦ Full pagewidth print                                           heads impractical                                                  without difficulty                                                                          due to actuator size                                             ♦ Does not require electrical                                     poling                                                  Ferroelectric                                                                        An electric field is used to induce a                                                          ♦ Low power consumption                                                       ♦ Difficult to integrate                                         with electronis   ♦                                                                IJ04                            phase transition between the                                                                   ♦ Many ink types can be                                                       ♦ Unusual materials such                                         as PLZSnT                                         antiferroelectric (AFE) and                                                                    ♦ Fast operation (<1                                                           are required                                     ferroelectric (FE) phase. Perovskite                                                           ♦ Relatively high longitudinal                                                ♦ Actuators require a                                            large area                                        materials such as tin modified lead                                                             strain                                                        lanthanum zirconate titanate                                                                   ♦ High efficiency                                (PLZSnT) exhibit large strains of up                                                           ♦ Electric field strength of                     to 1% associated with the AFE to FE                                                             around 3 V/μm can be                                       phase transition.                                                                               readily provided                                        Electrostatic                                                                        Conductive plates are separated by a                                                           ♦ Low power consumption                                                       ♦ Difficult to operate                                           electrostatic     ♦                                                                IJ02, IJ04                plates                                                                               compressible or fluid dielectric                                                               ♦ Many ink types can be                                                        devices in an aqueous environment                (usually air). Upon application of a                                                           ♦ Fast operation                                                              ♦ The electrostatic                                              acutator will                                     voltage, the plates attract each other                                                                       normally need to be separated from               and displace ink, causing drop                                                                               the ink                                          ejection. The conductive plates may                                                                         ♦ Very large area                                                required to achieve                               be in a comb or honeycomb     high forces                                      structure, or stacked to increase the                                                                       ♦ High voltage drive                                             transistors may be                                surface area and therefore the force.                                                                        required                                                                      ♦ Full pagewidth print                                           heads are not                                                                   competitive due to actuator size           Electrostatic                                                                        A strong electric field is applied to                                                          ♦ Low current consumption                                                     ♦ High voltage                                                                     ♦ 1989                                                           Saito et al,              pull on ink                                                                          the ink, whereupon electrostatic                                                               ♦ Low temperature                                                             ♦ May be damaged by                                              sparks due to air  U.S. Pat. No.                  attraction accelerates the ink towards                                                                       breakdown         4,799,068                      the print medium.            ♦ Requires field                                                 strength increases as                                                                            ♦ 1989                                                           Miura et al,                                                  the drop size decreases                                                                          U.S. Pat. No.                                               ♦ High voltage drive                                             transistors required                                                                              4,810,954                                                   ♦ Electrostatic field                                            attracts dust     ♦                                                                Tone-jet                  Permanent                                                                            An electromagnet directly attracts a                                                           ♦ Low power consumption                                                       ♦ Complex                                                                          ♦                                                                IJ07, IJ10                magnet                                                                               permanent magnet, displacing ink                                                               ♦ Many ink types can be                                                       ♦ Permanent magnetic                                             materials such as                           electro-                                                                             and cuasing drop ejection. Rare earth                                                          ♦ Fast operation                                                               Neodymium Iron Boride (NdFeB)              magnetic                                                                             magnets with a field strength around                                                           ♦ High efficiency                                                              required.                                        1 Tesla can be used. Examples are:                                                             ♦ Easy extension from                                                         ♦ High local currents                                            required                                          Samarium Cobalt (SaCo) and                                                                      nozzles to pagewidth print                                                                 ♦ Copper metalization                                            should be used                                    magnetic materials in the                                                                       heads        for long electromigration lifetime               neodymium iron boron family   and low resistivity                              (NdFeB, NdDyFeBNb, NdDyFeB,  ♦ Pigmented inks are                                             usually infeasible                                etc)                         ♦ Operating temperature                                          limited to the                                                                  Curie temperature (around 540 K)           Soft  A solenoid induced a magnetic field                                                            ♦ Low power consumption                                                       ♦ Complex                                                                          ♦                                                                IJ01, IJ05, IJ08,         magnetic                                                                             in a soft magnetic core or yoke                                                                ♦ Many ink types can be                                                       ♦ Materials not usually                                          present in a       IJ10                     core electro-                                                                        fabricated from a ferrous material                                                             ♦ Fast operation                                                               CMOS fab such as NiFe, CoNiFe,                                                                  ♦                                                                IJ12, IJ14, IJ15,         magnetic                                                                             such as electroplated iron alloys such                                                         ♦ High efficiency                                                              CoFe are required                                                                                IJ17                           as CoNiFe [1], CoFe, or NiFe alloys.                                                           ♦ Easy extension from                                                         ♦ High local currents                                            required                                          Typically, the soft magnetic material                                                           nozzles to pagewidth print                                                                 ♦ Copper metalization                                            should be used                                    is in two parts, which are normally                                                             heads        for long electromigration lifetime               held apart by a spring. When the                                                                             and low resistivity                              solenoid is actuated, the two parts                                                                         ♦ Electroplating is                                              required                                          attract, displacing the ink. ♦ High saturation flux                                           density is                                                                      required (2.0-2.1 T is achievable                                              with CoNiFe [1])                           Magnetic                                                                             The Lorenz force acting on a current                                                           ♦ Low power consumption                                                       ♦ Force acts as a                                                twisting motion   ♦                                                                IJ06, IJ11, IJ13,         Lorenz                                                                               carrying wire in a magnetic field is                                                           ♦ Many ink types can be                                                       ♦ Typically, only a                                              quarter of the     IJ16                     force utilized.       ♦ Fast operation                                                               solenoid length provides force in a              This allows the magnetic field to be                                                           ♦ High efficiency                                                              useful direction                                 supplied externally to the print head,                                                         ♦ Easy extension from                                                         ♦ High local currents                                            required                                          for example with rare earth                                                                     nozzles to pagewidth print                                                                 ♦ Copper metalization                                            should be used                                    permanent magnets.                                                                              heads        for long electromigration lifetime               Only the current carrying wire need                                                                          and low resistivity                              be fabricated on the print-head,                                                                            ♦ Pigmented inks are                                             usually infeasible                                simplifying materials requirements.                                      Magneto-                                                                             The actuator uses the giant                                                                    ♦ Many ink types can be                                                       ♦ Force acts as a                                                twisting motion   ♦                                                                Fischenbeck, U.S.         striction                                                                            magnetostrictive effect of materials                                                           ♦ Fast operation                                                              ♦ Unusual materials such                                         as Terfenol-D      Pat. No. 4,032,929             such as Terfenol-D (an alloy of                                                                ♦ Easy extension from                                                          are required     ♦                                                                IJ25                            terbium, dysprosium and iron                                                                    nozzles to pagewidth print                                                                 ♦ High local currents                                            required                                          developed at the Naval Ordnance                                                                 heads       ♦ Copper metalization                                            should be used                                    Laboratory, hence Ter-Fe-NOL). For                                                             ♦ High force is available                                                      for long electromigration lifetime               best efficiency, the actuator should                                                                         and low resistivity                              be pre-stressed to approx. 8 MPa.                                                                           ♦ Pre-stressing may be                                           required                                    Surface                                                                              Ink under positive pressure is held in                                                         ♦ Low power consumption                                                       ♦ Requires supplementary                                         force to          ♦                                                                Silverbrook, EP           tension                                                                              a nozzle by surface tension. The                                                               ♦ Simple construction                                                          effect drop separation                                                                           0771 658 A2 and          reduction                                                                            surface tension of the ink is reduced                                                          ♦ No unusual materials                                                        ♦ Requires special ink                                           surfactants        related patent                 below the bubble threshold, causing                                                             required in fabrication                                                                    ♦ Speed may be limited                                           by surfactant      applications                   the ink to egress from the nozzle.                                                             ♦ High efficiency                                                              properties                                                       ♦ Easy extension from single                                      nozzles to pagewidth print                                                     heads                                                   Viscosity                                                                            The ink viscosity is locally reduced                                                           ♦ Simple construction                                                         ♦ Requires supplementary                                         force to          ♦                                                                Silverbrook, EP           reduction                                                                            to select which drops are to be                                                                ♦ No unusual materials                                                         effect drop separation                                                                           0771 658 A2 and                ejected. A viscosity reduction can be                                                           required in fabrication                                                                    ♦ Requires special ink                                           viscosity          related patent                 achieved electrothermally with most                                                            ♦ Easy extension from                                                          properties        application                    inks, but special inks can be                                                                   nozzles to pagewidth print                                                                 ♦ High speed is                                                  difficult to achieve                              engineered for a 100:1 viscosity                                                                heads       ♦ Requires oscillating                                           ink pressure                                      reduction.                   ♦ A high temperature                                             difference                                                                      (typically 80 degrees) is required         Acoustic                                                                             An acoustic wave is generated and                                                              ♦ Can operate without                                                         ♦ Complex drive                                                  circuitry         ♦ 1993                                                           Hadimioglu et                   focussed upon the drop ejection                                                                 nozzle plate                                                                               ♦ Complex                                                                           al, EUP 550,192                region.                      ♦ Low efficiency                                                                   ♦ 1993                                                           Elrod et al,                                                 ♦ Poor control of drop                                           position           EUP 572,230                                                 ♦ Poor control of drop                                           volume                                      Thermo-                                                                              An actuator which relies upon                                                                  ♦ Low power consumption                                                       ♦ Efficient aqueous                                              operation requires a                                                                             ♦                                                                IJ03, IJ09, IJ17,         elastic bend                                                                         differential thermal expansion upon                                                            ♦ Many ink types can be                                                        thermal insulator on the hot                                                                     IJ18                     actuator                                                                             Joule heating is used.                                                                         ♦ Simple planar fabrication                                                   ♦ Corrosion prevention                                           can be difficult  ♦                                                                IJ19, IJ20, IJ21,                               ♦ Small chip area required                                                    ♦ Pigmented inks may be                                          infeasible, as     IJ22                                            for each actuator                                                                           pigment particles may jam the                                                                   ♦                                                                IJ23, IJ24, IJ27,                               ♦ Fast operation                                                               actuator          IJ28                                           ♦ High efficiency                                                                               ♦                                                                IJ29, IJ30, IJ31,                               ♦ CMOS compatible voltages                                                                       IJ32                                            and currents                  ♦                                                                IJ33, IJ34, IJ35,                               ♦ Standard MEMS processes                                                                        IJ36                                            can be used                   ♦                                                                IJ37, IJ38, IJ39,                               ♦ Easy extension from                                                                            IJ40e                                           nozzles to pagewidth print    ♦                                                                IJ41                                             heads                                                   High CTE                                                                             A material with a very high                                                                    ♦ High force can be                                                           ♦ Requires special                                               material (e.g. PTFE)                                                                             ♦                                                                IJ09, IJ17, IJ18,         thermo-                                                                              coefficient of thermal expansion                                                                generated   ♦ Requires a PTFE                                                deposition process,                                                                               IJ20                     elastic                                                                              (CTE) such as   ♦ PTFE is a candidate                                                          which is not yet standard in                                                                    ♦                                                                IJ21, IJ22, IJ23,         acutator                                                                             polytetrafluoroethylene (PTFE) is                                                               low dielectric constant                                                                     fabs              IJ24                           used. As high CTE materials are                                                                 insulation in ULSI                                                                         ♦ PTFE deposition cannot                                         be followed       ♦                                                                IJ27, IJ28, IJ29,               usually non-conductive, a heater                                                               ♦ Very low power                                                               with high temperature                                                                            IJ30e                          fabricated from a conductive                                                                    consumption  350° C.) processing                                                                      ♦                                                                IJ31, IJ42, IJ43,               material is incorporated. A 50 μm                                                           ♦ Many ink types can                                                          ♦ Pigmented inks may be                                          infeasible, as     IJ44                           long PTFE bend actuator with                                                                    used         pigment particles may jam the bend               polysilicon heater and 15 mW power                                                             ♦ Simple planar fabrication                                                    actuator                                         input can provide 180 μN force and                                                          ♦ Small chip area required                       10 μm deflection. Actuator motions                                                           for each actuator                                             include:        ♦ Fast operation                                 Bend            ♦ High efficiency                                Push            ♦ CMOS compatible voltages                       Buckle           voltages and currents                                         Rotate          ♦ Easy extension from single                                      nozzles to pagewidth print                                                     heads                                                   Conductive                                                                           A polymer with a high coefficient of                                                           ♦ High force can be                                                           ♦ Requires special                                               materials         ♦                                                                IJ24                      polymer                                                                              thermal expansion (such as PTFE) is                                                             generated    development (High CTE conductive           thermo-                                                                              doped with conducting substances to                                                            ♦ Very low power                                                               polymer)                                   elastic                                                                              increase its conductivity to about 3                                                            consumption ♦ Requires a PTFE                                                deposition process,                         actuator                                                                             orders of magnitude below that of                                                              ♦ Many ink types can                                                           which is not yet standard in ULSI                copper. The conducting polymer                                                                  used         fabs                                             expands when resistively heated.                                                               ♦ Simple planar fabrication                                                   ♦ PTFE deposition cannot                                         be followed                                       Examples of conducting dopants                                                                 ♦ Small chip area required                                                     with high temperature (above                     include:         for each actuator                                                                           350° C.) processing                       1) Carbon nanotubes                                                                            ♦ Fast operation                                                              ♦ Evaporation and CVD                                            deposition                                        2) Metal fibers ♦ High efficiency                                                              techniques cannot be used                        3) Conductive polymers such as                                                                 ♦ CMOS compatible voltages                                                    ♦ Pigmented inks may be                                          feasible, as                                      doped polythiophene                                                                             and currents                                                                                pigment particles may jam the bend               4) Carbon granules                                                                             ♦ Easy extension from                                                          actuator                                                          nozzles to pagewidth print                                                     heads                                                   Shape A shape memory alloy such as TiNi                                                              ♦ High force is available                                                     ♦ Fatigue limits maximum                                         number of         ♦                                                                IJ26                      memory                                                                               (also known as Nitinol - Nickel                                                                 (stresses of hundreds of                                                                    cycles                                     alloy Titanium alloy developed at the                                                                 MPa)        ♦ Low strain (1%) is                                             required to extend                                Naval Ordnance Laboratory) is                                                                  ♦ Large strain is available                                                    fatigue resistance                               thermally switched between its weak                                                             (more than 3%)                                                                             ♦ Cycle rate limited by                                          heat removal                                      martensitic state and its high                                                                 ♦ High corrosion resistance                                                   ♦ Requires unusual                                               materials (TiNi)                                  stiffness austenic state. The shape of                                                         ♦ Simple construction                                                         ♦ The latent heat of                                             transformation                                    the actuator in its martensitic state is                                                       ♦ Easy extension from                                                          must be provided                                 deformed relative to the austenic                                                               nozzles to pagewdith print                                                                 ♦ High current operation            shape. The shape change causes                                                                  heads       ♦ Requires pre-stressing                                         to distort the                                    ejection of a drop.                                                                            ♦ Low voltage operation                                                        martensitic state                          Linear                                                                               Linear magnetic actuators include                                                              ♦ Linear Magnetic actuators                                                   ♦ Requires unusual                                               semiconductor     ♦                                                                IJ12                      Magnetic                                                                             the Linear Induction Actuator (LIA),                                                            can be constructed with                                                                     materials such as soft magnetic                                               alloys                                      Actuator                                                                             Linear Permanent Magnet                                                                         high thrust, long travel, and                                                               (e.g. CoNiFe [1])                                Synchronous Actuator (LPMSA),                                                                   high efficiency using planar                                                               ♦ Some varieties also                                            require permanent                                 Linear Reluctance Synchronous                                                                   semiconductor fabrication                                                                   magnetic materials such as                       Actuator (LRSA), Linear Switched                                                                techniques   Neodymium iron boron (NdFeB)                     Reluctance Actuator (LSRA), and                                                                ♦ Long actuator travel                                                        ♦ Requires complex                                               multi-phase drive                                 the Linear Stepper Actuator (LSA).                                                              available    circuitry                                                        ♦ Medium force is available                                                   ♦ High current operation                            ♦ Low voltage operation                    __________________________________________________________________________

    __________________________________________________________________________     BASIC OPERATION MODE                                                           Description           Advantages   Disadvantages    Examples                   __________________________________________________________________________     Actuator                                                                             This is the simplest mode of                                                                   ♦ Simple operation                                                            ♦ Drop repetition rate                                           is usually limited                                                                              ♦                                                                Thermal inkjet             directly                                                                             operation: the actuator directly                                                               ♦ No external fields                                                           to less than 10 KHz. However, this                                                             ♦                                                                Piezoelectric inkjet       pushes ink                                                                           supplies sufficient kinetic energy to                                                          ♦ Satellite drops can                                                          not fundamental to the method, but                                                             ♦ IJ01,                                                          IJ02, IJ03, IJ04                 expel the drop. The drop must have a                                                            avoided if drop velocity is                                                                 related to the refill method                                                                   ♦ IJ05,                                                          IJ06, IJ07, IJ09                 sufficient velocity to overcome the                                                             less than 4 m/s                                                                             used            ♦ IJ11,                                                          IJ12, IJ14, IJ16                 surface tension.                                                                               ♦ Can be efficient,                                                           ♦ All of the drop                                                kinetic energy must                                                                             ♦ IJ20,                                                          IJ22, IJ23, IJ24                                  upon the actuator used                                                                      be provided by the actuator                                                                    ♦ IJ25,                                                          IJ26, IJ27, IJ28                                              ♦ Satellite drops                                                usually form if drop                                                                            ♦ IJ29,                                                          IJ30, IJ31, IJ32                                               velocity is greater than 4.5                                                                   ♦ IJ33,                                                          IJ34, IJ35, IJ36                                                               ♦ IJ37,                                                          IJ38, IJ39, IJ40                                                               ♦ IJ41,                                                          IJ42, IJ43, IJ44           Proximity                                                                            The drops to be printed are selected                                                           ♦ Very simple print                                                           ♦ Requires close                                                 proximity between the                                                                           ♦                                                                Silverbrook, EP                  by some manner (e.g. thermally                                                                  fabrication can be used                                                                     print head and the print media                                                                  0771 658 A2 and                 induced surface tension reduction of                                                           ♦ The drop selection                                                           transfer roller  related patent                  pressurized ink). Selected drops are                                                            does not need to provide                                                                   ♦ May require two print                                          heads printing    applications                    separated from the ink in the nozzle                                                            the energy required to                                                                      alternate rows of the image                      by contact with the print medium or                                                             separate the drop from the                                                                 ♦ Monolithic color print                                         heads are                                         a transfer roller.                                                                              nozzle       difficult                                  Electrostatic                                                                        The drops to be printed are selected                                                           ♦ Very simple print                                                           ♦ Requires very high                                             electrostatic field                                                                             ♦                                                                Silverbrook, EP            pull on ink                                                                          by some manner (e.g. thermally                                                                  fabricaton can be used                                                                     ♦ Electrostatic field                                            for small nozzle  0771 658 A2 and                 induced surface tension reduction of                                                           ♦ The drop selection                                                           sizes is above air breakdown                                                                    related patent                  pressurized ink). Selected drops are                                                            does not need to provide                                                                   ♦ Electrostatic field                                            may attract dust  applications                    separated from the ink in the nozzle                                                            the energy required to       ♦                                                                Tone-Jet                         by a strong electric field.                                                                     separate the drop from the                                                     nozzle                                                  Magnetic                                                                             The drops to be printed are selected                                                           ♦ Very simple print                                                           ♦ Requires magnetic                                                               ♦                                                                Silverbrook, EP            pull on ink                                                                          by some manner (e.g. thermally                                                                  fabrication can be used                                                                    ♦ Ink colors other than                                          black are         0771 658 A2 and                 induced surface tension reduction of                                                           ♦ The drop selection                                                           difficult        related patent                  pressurized ink). Selected drops are                                                            does not need to provide                                                                   ♦ Requires very high                                             magnetic fields   applications                    separated from the ink in the nozzle                                                            the energy required to                                        by a strong magnetic field acting on                                                            separate the drop from the                                    the magnetic ink.                                                                               nozzle                                                  Shutter                                                                              The actuator moves a shutter to                                                                ♦ High speed (>50 KHz)                                                        ♦ Moving parts are                                               required         ♦ IJ13,                                                          IJ17, IJ21                       block ink flow to the nozzle. The ink                                                           operation can be achieved                                                                  ♦ Requires ink pressure                                          modulator                                         pressure is pulsed at a multiple of the                                                         due to reduced refill time                                                                 ♦ Friction and wear must                                         be considered                                     drop ejection frequency.                                                                       ♦ Drop timing cay be                                                          ♦ Stiction is possible                               accurate                                                                      ♦ The actuator energy can be                                      very low                                                Shuttered                                                                            The actuator moves a shutter to                                                                ♦ Actuators wil small                                                         ♦ Moving parts are                                               required         ♦ IJ08,                                                          IJ15, IJ18, IJ19           grill block ink flow through a grill to the                                                           can be used ♦ Requires ink pressure                                          modulator                                         nozzle. The shutter movement need                                                              ♦ Actuators with small                                                        ♦ Friction and wear must                                         be considered                                     only be equal to the width of the grill                                                         can be used ♦ Stiction is possible              holes.          ♦ High speed (>50 KHz)                                            operation can be achieved                               Pulsed                                                                               A pulsed magnetic field attracts an                                                            ♦ Extremely low energy                                                        ♦ Requires an external                                           pulsed magnetic  ♦ IJ10       magnetic                                                                             `ink pusher` at the drop ejection                                                               operation is possible                                                                       field                                      pull on ink                                                                          frequency. An actuator controls a                                                              ♦ No heat dissipation                                                         ♦ Requires special                                               materials for both                          pusher                                                                               catch, which prevents the ink pusher                                                            problems     the actuator and the ink pusher                  from moving when a drop is not to                                                                           ♦ Complex construction              be ejected.                                                              __________________________________________________________________________

    __________________________________________________________________________     AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES)                                   Description           Advantages   Disadvantages    Examples                   __________________________________________________________________________     None  The actuator directly fires the ink                                                            ♦ Simplicity of construction                                                  ♦ Drop ejection energy                                           must be          ♦ Most                                                           inkjets,                         drop, and there is no external field or                                                        ♦ Simplicity of operation                                                      supplied by individual nozzle                                                 actuator          including                       other mechanism required.                                                                      ♦ Small physical size                                                                           piezoelectric and                                                              thermal bubble.                                                               ♦                                                                IJ01-IJ07, IJ09,                                                               IJ11                                                                           ♦ IJ12,                                                          IJ14, IJ20, IJ22                                                               ♦                                                                IJ23-IJ45                  Oscillating                                                                          The ink pressure oscillates,                                                                   ♦ Oscillating ink pressure                                                    ♦ Requires external ink                                          pressure         ♦                                                                Silverbrook, EP            ink pressure                                                                         providing much of the drop ejection                                                             provide a refill pulse,                                                                     oscillator       0771 658 A2 and           (including                                                                           energy. The actuator selects which                                                              allowing higher operating                                                                  ♦ Ink pressure phase and                                         amplitude         related patent            acoustic                                                                             drops are to be fired by selectively                                                            speed        must be carefully controlled                                                                    applications              stimulation)                                                                         blocking or enabling nozzles. The                                                              ♦ The actuators may                                                           ♦ Acoustic reflections                                           in the ink       ♦ IJ08,                                                          IJ13, IJ15, IJ17                 ink pressure oscillation may be                                                                 with much lower energy                                                                      chamber must be designed                                                                       ♦ IJ18,                                                          IJ19, IJ21                       achieved by vibrating the print head,                                                          ♦ Acoustic lenses can be used                    or preferably by an actuator in the                                                             to focus the sound on the                                     ink supply.      nozzles                                                 Media The print head is placed in close                                                              ♦ Low power                                                                   ♦ Precision assembly                                             required         ♦                                                                Silverbrook, EP            proximity                                                                            proximity to the print medium.                                                                 ♦ High accuracy                                                               ♦ Paper fibers may cause                                         problems          0771 658 A2 and                 Selected drops protrude from the                                                               ♦ Simple print head                                                           ♦ Cannot print on rough                                          substrates        related patent                  print head further than unselected                                                              construction                  applications                    drops, and contact the print medium.                                           The drop soaks into the medium fast                                            enough to cause drop separation.                                         Transfer                                                                             Drops are printed to a transfer roller                                                         ♦ High accuracy                                                               ♦ Bulky                                                                           ♦                                                                Silverbrook, EP            roller                                                                               instead of straight to the print                                                               ♦ Wide range of print                                                         ♦ Expensive                                                                        0771 658 A2 and                 medium. A transfer roller can also be                                                           substrates can be used                                                                     ♦ Complex                                                                          related patent                  used for proximity drop separation.                                                            ♦ Ink can be dried on                                                                           applications                                     transfer roller              ♦                                                                Tektronix hot melt                                                              piezeoelectric                                                                inkjet                                                                         ♦ Any                                                            of the IJ series           Electrostatic                                                                        An electric field is used to accelerate                                                        ♦ Low power                                                                   ♦ Field strength                                                 required for separation                                                                         ♦                                                                Silverbrook, EP                  selected drops towards the print                                                               ♦ Simple print head                                                            of small drops is near or above                                                                 0771 658 A2 and                 medium.          construction                                                                                breakdown        related patent                                                                 applications                                                                  ♦                                                                Tone-Jet                   Direct                                                                               A magnetic field is used to accelerate                                                         ♦ Low power                                                                   ♦ Requires magnetic                                                               ♦                                                                Silverbrook, EP            magnetic                                                                             selected drops of magnetic ink                                                                 ♦ Simple print head                                                           ♦ Requires strong                                                magnetic field    0771 658 A2 and           field towards the print medium.                                                                       construction                  related patent                                                                 applications              Cross The print head is placed in a constant                                                         ♦ Does not require magnetic                                                   ♦ Requires external                                              magnet           ♦ IJ06,                                                          IJ16                       magnetic                                                                             magnetic field. The Lorenz force in a                                                           materials to be integrated in                                                              ♦ Current densities may                                          be high,                                    field current carrying wire is used to move                                                           the print head                                                                              resulting in electromigration                    the actuator.    manufacturing process                                                                       problems                                   Pulsed                                                                               A pulsed magnetic field is used to                                                             ♦ Very low power operation                                                    ♦ Complex print head                                             construction     ♦ IJ10       magnetic                                                                             cyclically attract a paddle, which                                                              is possible ♦ Magnetic matierals                                             required in print                           field pushes on the ink. A small actuator                                                            ♦ Small print head size                                                        head                                             moves a catch, which selectively                                               prevents the paddle from moving.                                         __________________________________________________________________________

    __________________________________________________________________________     ACTUATOR AMPLIFICATION OR MODIFICATION METHOD                                  Description           Advantages    Disadvantages    Examples                  __________________________________________________________________________     None  No actuator mechanical                                                                         ♦ Operational simplicity                                                       ♦ Many actuator                                                  mechanisms have  ♦                                                                Thermal Bubble                  amplification is used. The actuator                                                                           insufficient travel, or                                                                         Inkjetcient                    directly drives the drop ejection                                                                             force, to efficiently drive the                                                                ♦                                                                IJ01, IJ02, IJ06,               process.                       ejection process                                                                                IJ07                     Differential                                                                         An acutator material expands more                                                              ♦ Provides greater travel in                                                   ♦ High stresses are                                              involved         ♦                                                                IJ16, IJ25, IJ26          expansion                                                                            on one side than on the other. The                                                              reduced print head area                                                                     ♦ Care must be taken                                             that the materials                                                                              ♦                                                                Piezoelectric             bend  expansion may be thermal,                                                                      ♦ The bend actuator                                                             do not delaminate                                                                              ♦                                                                IJ03, IJ09, IJ17-         actuator                                                                             piezoelectric, magnetostrictive, or                                                             a high force low travel                                                                     ♦ Residual bend                                                  resulting from high                                                                              IJ24                           other mechanism.                                                                                actuator mechanism to high                                                                   temperature or high stress                                                                     ♦                                                                IJ27, IJ29-IJ39,                                 travel, lower force                                                                          formation       ♦                                                                IJ42, IJ43, IJ44                                 mechanism.                                              Transient                                                                            A trilayer bend actuator where the                                                             ♦ Very good temperature                                                        ♦ High stresses are                                              involved         ♦                                                                IJ40, IJ41                bend  two outside layers are identical. This                                                          stability    ♦ Care must be taken                                             that the materials                         actuator                                                                             cancels bend due to ambient                                                                    ♦ High speed, as a new                                                          do not delaminate                               temperature and reesidual stress. The                                                           can be fired before heat                                      actuator only responds to transient                                                             dissipates                                                    heating of one side or the other.                                                              ♦ Cancels residual stress of                                      formation                                               Reverse                                                                              The actuator loads a spring. When                                                              ♦ Better coupling to the                                                       ♦ Fabrication                                                    complexity       ♦                                                                IJ05, IJ11                spring                                                                               the actuator is turned off, the spring                                                                       ♦ High stress in the                                             spring                                           releases. This can reverse the                                                 force/distance curve of the actuator                                           to make it compatible with the                                                 force/time requirements of the drop                                            ejection.                                                                Actuator                                                                             A series of thin actuators are stacked.                                                        ♦ Increased travel                                                             ♦ Increased fabrication                                          complexity       ♦ Some                                                           piezoelectric             stack This can be appropriate where                                                                  ♦ Reduced drive voltage                                                        ♦ Increased possibility                                          of short circuits                                                                                ink jets                       actuators require high electric field                                                                         due to pinholes ♦                                                                IJ04                            strength, such as electrostatic and                                            piezoelectric actuators.                                                 Multiple                                                                             Multiple smaller actuators are used                                                            ♦ Increase the force                                                           ♦ Actuator forces may                                            not add linearly,                                                                               ♦                                                                IJ12, IJ13, IJ18,         actuators                                                                            simultaneously to move the ink.                                                                 from an actuator                                                                             reducing efficiency                                                                             IJ20                           Each actuator need provide only a                                                              ♦ Multiple actuators can                                                                        ♦                                                                IJ22, IJ28, IJ42,               portion of the force required.                                                                  positioned to control ink      IJ43                                            flow accurately                                         Linear                                                                               A linear spring is used to transform a                                                         ♦ Matches low travel                                                           ♦ Requires print head                                            area for the     ♦                                                                IJ15                      Spring                                                                               motion with small travel and high                                                               spring with higher travel                                     force into a longer travel, lower force                                                         requirements                                                  motion.         ♦ Non-contact method of                                           motion transformation                                   Coiled                                                                               A bend actuator is coiled to provide                                                           ♦ Increases travel                                                             ♦ Generally restricted                                           to               ♦                                                                IJ17, IJ21, IJ34,         actuator                                                                             greater travel in a reduced chip area.                                                         ♦ Reduces chip area                                                             planar implementations due                                                                      IJ35                                           ♦ Planar implementations                                                        extreme fabrication difficulty in                                             other                                                             relatively easy to fabricate.                                                                orientations.                             Flexure bend                                                                         A bend actuator has a small region                                                             ♦ Simple means of increasing                                                   ♦ Care must be taken                                             not to exceed the                                                                               ♦                                                                IJ10, IJ19, IJ33          actuator                                                                             near the fixture point, which flexes                                                            travel of a bend actuator                                                                    elastic limit in the flexure area               much more readily than the    ♦ Stress distribution                                            is very uneven                                   remainder of the actuator. The                                                                               ♦ Difficult to                                                   accurately model with                            actuator flexing is effectively                                                                               finite element analysis                         converted from an even coiling to an                                           angular bend, resulting in greater                                             travel of the actuator tip.                                              Catch The actuator controls a small catch.                                                           ♦ Very low actuator                                                            ♦ Complex                                                                         ♦                                                                IJ10                            The catch either enables or disables                                                           ♦ Very small actuator                                                          ♦ Requires external                                              force                                            movement of an ink pusher that is                                                                            ♦ Unsuitable for                                                 pigmented inks                                   controlled in a bulk manner.                                             Gears Gears can be used to increase travel                                                           ♦ Low force, low travel                                                        ♦ Moving parts are                                               required         ♦                                                                IJ13                            at the expense of duration. Circular                                                            actuators can be used                                                                       ♦ Several actuator                                               cycles are required                              gears, rack and pinion, ratchets, and                                                          ♦ Can be fabricated                                                            ♦ More complex drive                                             electronics                                      other gearing methods can be used.                                                              standard surface MEMS                                                                       ♦ Complex construction                              processes    ♦ Friction, friction,                                            and wear are                                                                    possible                                  Buckle plate                                                                         A buckle plate can be used to change                                                           ♦ Very fast movement                                                           ♦ Must stay within                                               elastic limits of the                                                                           ♦ S.                                                             HIrata et al, "An               a slow actuator into a fast motion. It                                                          achievable    materials for long device                                                                       Ink-jet Head . .                                                              .",                             can also convert a high force, low                                                                           ♦ High stresses                                                  involved          Proc. IEEE MEMS,               travel actuator into a high travel,                                                                          ♦ Generally high power                                           requirement       Feb. 1996, pp 418-             medium force motion.                            423.                                                                          ♦                                                                IJ18, IJ27                Tapered                                                                              A tapered magnetic pole can increase                                                           ♦ Linearizes the magnetic                                                      ♦ Complex                                                                         ♦                                                                IJ14                      magnetic                                                                             travel at the expense of force.                                                                 force/distance curve                                    pole                                                                           Lever A lever and fulcrum is used to                                                                 ♦ Matches low travel                                                           ♦ High stress around                                             the fulcrum      ♦                                                                IJ32, IJ36, IJ37                transform a motion with small travel                                                            with higher travel                                            and high force into a motion with                                                               requirements                                                  longer travel and lower force. The                                                             ♦ Fulcrum are has no linear                      lever can also reverse the direction of                                                         movement, and can be used                                     travel.          for a fluid seal                                        Rotary                                                                               The actuator is connected to a rotary                                                          ♦ High mechanical advantage                                                    ♦ Complex                                                                         ♦                                                                IJ28                      impeller                                                                             impeller. A small angular deflection                                                           ♦ The ratio of force to                                                        ♦ Unsuitable for                                                 pigmented inks                                   of the actuator results in a rotation of                                                        of the actuator can be                                        the impeller vanes, which push the                                                              matched to the nozzle                                         ink against stationary vanes and out                                                            requirements by varying the                                   of the nozzle.   number of impeller vanes                                Acoustic                                                                             A refractive or diffractive (e.g. zone                                                         ♦ No moving parts                                                              ♦ Large area                                                                      ♦ 1993                                                           Hadimioglu et             lens  plate) acoustic lens is used to                                                                              ♦ Only relevant for                                              acoustic ink jets                                                                                al, EUP 550,192                concentrate sound waves.                       ♦ 1993                                                           Elrod et al,                                                                    EUP 572,220              Sharp A sharp point is used to concentrate                                                           ♦ Simple construction                                                          ♦ Difficult to                                                   fabricate using standard                                                                        ♦                                                                Tone-jet                  conductive                                                                           an electrostatic field.        VLSI processes for a surface                                                  ejecting                                   point                                ink-jet                                                                       ♦ Only relevant for                                              electrostatic ink jets                     __________________________________________________________________________

    __________________________________________________________________________     ACTUATOR MOTION                                                                Description           Advantages   Disadvantages     Examples                  __________________________________________________________________________     Volume                                                                               The volume of the actuator changes,                                                            ♦ Simple constuction in                                                       ♦ High energy is                                                 typically required to                                                                            ♦                                                                Hewlett-Packard           expansion                                                                            pushing the ink in all directions.                                                              case of thermal ink jet                                                                     achieve volume expansion. This                                                                   Thermal Inkjet                                               to thermal stress, cavitation,                                                                  ♦                                                                Canon Bubblejet                                               kogation in thermal ink jet                                                    implementations                            Linear,                                                                              The actuator moves in a direction                                                              ♦ Efficient coupling to                                                       ♦ High fabrication                                               complexity may be ♦                                                                IJ01, IJ02, IJ04,         normal to                                                                            normal to the print head surface. The                                                           drops ejected normal to the                                                                 required to achieve                                                                              IJ07ndicular             chip surface                                                                         nozzle is typically in the line of                                                              surface      motion           ♦                                                                IJ11, IJ14                      movement.                                                                Parallel to                                                                          The actuator moves parallel to the                                                             ♦ Suitable for planar                                                         ♦ Fabrication                                                                      ♦                                                                IJ12, IJ13, IJ15,         chip surface                                                                         print head surface. Drop ejection                                                               fabrication ♦ Friction                                                                          IJ33,                          may still be normal to the surface.                                                                         ♦ Stiction                                                                         ♦                                                                IJ34, IJ35, IJ36          Membrane                                                                             An actuator with a high force but                                                              ♦ The effective area of                                                       ♦ Fabrication                                                                      ♦ 1982                                                           Howkins U.S.              push  small area is used to push a stiff                                                              actuator becomes the                                                                       ♦ Actuator                                                                          Pat. No. 4,459,601             membrane that is in contact with the                                                            membrane area                                                                              ♦ Difficulty of                                                  integration in a VLSI                             ink.                          process                                    Rotary                                                                               The actuator causes the rotation of                                                            ♦ Rotary levers may be                                                        ♦ Device                                                                           ♦                                                                IJ05, IJ08, IJ13,               some element, such a grill or                                                                   to increase travel                                                                         ♦ May have friction at a                                         pivot point        IJ28                           impeller        ♦ Small chip area                                                 requirements                                            Bend  The actuator bends when energized.                                                             ♦ A very small change                                                         ♦ Requires the actuator                                          to be made from   ♦ 1970                                                           Kyser et al                     This may be due to differential                                                                 dimensions can be                                                                           at least two distinct layers, or to                                           have               U.S. Pat.                      thermal expansion, piezoelectric                                                                converted to a large motion.                                                                a thermal difference across                                                                      No. 3,946,398                  expansion, magnetostriction, or other                                                                        actuator         ♦                                                                IJ03, IJ09, IJ10,               form of relative dimensional change.            IJ19                                                                          ♦                                                                IJ23, IJ24, IJ25,                                                               IJ29                                                                          ♦                                                                IJ30, IJ31, IJ33,                                                               IJ34                                                                          ♦                                                                IJ35                      Swivel                                                                               The actuator swivel around a central                                                           ♦ Allows operation where                                                      ♦ Inefficient coupling                                           to the ink motion ♦                                                                IJ06                            pivot. This motion is suitable where                                                            net linear force on the                                       there are opposite forces applied to                                                            paddle is zero                                                opposite sides of the paddle, e.g.                                                             ♦ Small chip area                                Lorenz force.    requirements                                            Straighten                                                                           The actuator is normally bent, and                                                             ♦ Can be used with shape                                                      ♦ Requires careful                                               balance of stresses to                                                                           ♦                                                                IJ26, IJ32                      straightens when energized.                                                                     memory allows where the                                                                     ensure that the quiescent bend is                                 austenic phase is planar                                                                    accurate                                   Double                                                                               The actuator bends in one direction                                                            ♦ One actuator can be used                                                    ♦ Difficult to make the                                          drops ejected by  ♦                                                                IJ36, IJ37, IJ38          bend  when one element is energized, and                                                              power two nozzles.                                                                          both bend directions identical.                  bends the other way when another                                                               ♦ Reduced chip size.                                                          ♦ A small efficiency                                             loss compared to                                  element is energized.                                                                          ♦ Not sensitive to ambient                                                     equivalent single bend actuators.                                 temperature                                             Shear Energizing the actuator causes a                                                               ♦ Can increase the effective                                                  ♦ Not readily applicable                                         to other          ♦ 1985                                                           Fishbeck                        shear motion in the actuator material.                                                          actuator travel of piezo-                                                                   mechanisms        U.S. Pat.                                       electric actuators             No. 4,584,590            Radial                                                                               The actuator squeezes an ink                                                                   ♦ Relatively easy to                                                          ♦ High force                                                                       ♦ 1970                                                           Zoltan U.S.               constriction                                                                         reservoir, forcing ink from a                                                                   single nozzles from glass                                                                  ♦ Inefficient                                                                       Pat. No. 3,683,212             constricted nozzle.                                                                             tubing as macroscopic                                                                      ♦ Difficult to integrate                                         with VLSI                                                          structures   processes                                  Coil/uncoil                                                                          A coiled actuator uncoils or coils                                                             ♦ Easy to fabricate as                                                        ♦ Difficult to fabricate                                         for non-planar    ♦                                                                IJ17, IJ21, IJ34,               more tightly. The motion of the free                                                            planar VLSI process                                                                         devices           IJ35                           end of the actuator ejects the ink.                                                            ♦ Small area required,                                                        ♦ Poor out-of-plane                                              stiffness                                                          therefore low cost                                      Bow   The actuator bows (or buckles) in the                                                          ♦ Can increase the speed                                                      ♦ Maximum travel is                                              constrained       ♦                                                                IJ16, IJ18, IJ27                middle when energized.                                                                          travel      ♦ High force required                               ♦ Mechanically rigid                       Push-Pull                                                                            Two actuators control a shutter. One                                                           ♦ The structure is pinned                                                     ♦ Not readily suitable                                           for inkjets which ♦                                                                IJ18                            actuator pulls the shutter, and the                                                             both ends, so has a high                                                                    directly push the ink                            other pushes it.                                                                                out-of-plane rigidity                                   Curl inwards                                                                         A set of actuators curl inwards to                                                             ♦ Good fluid flow to                                                          ♦ Design                                                                           ♦                                                                IJ20, IJ42                      reduce the volume of ink that they                                                              region behind the actuator                                    enclose.         increases efficiency                                    Curl  A set of actuators curl outwards,                                                              ♦ Relatively simple                                                           ♦ Relatively large chip                                          are               ♦                                                                IJ22                      outwards                                                                             pressurizing ink in a chamber                                                                   construction                                                  surrounding the actuators, and                                                 expelling ink from a nozzle in the                                             chamber.                                                                 Iris  Multiple vanes enclose a volume of                                                             ♦ High efficiency                                                             ♦ High fabrication                                               complexity        ♦                                                                IJ22                            ink. These simultabeously rotate,                                                              ♦ Small chip area                                                             ♦ Not suitable for                                               pigmented inks                                    reducing the volume between the                                                vanes.                                                                   Acoustic                                                                             The actuator vibrates at a high                                                                ♦ The actuator can be                                                         ♦ Large area required                                            for efficient     ♦ 1993                                                           Hadimioglu et             vibration                                                                            frequency.       physically distant from the                                                                 operation at useful                                                                              et al, EUP 550,192                              ink         ♦ Acoustic coupling and                                          crosstalk         ♦ 1993                                                           Elrod et al,                                                 ♦ Complex drive                                                  circuitry          EUP 572,220                                                 ♦ Poor control of drop                                           volume and                                                                      position                                   None  In various ink jet designs the actuator                                                        ♦ No moving parts                                                             ♦ Various other                                                  tradeoffs are required                                                                           ♦                                                                Silverbrook, EP                 does not move.                eliminate moving parts                                                                           0771 648 A2 and                                                                related patent                                                                 applications                                                                  ♦                                                                Tone-jet                  __________________________________________________________________________

    __________________________________________________________________________     NOZZLE REFILL METHOD                                                           Description           Advantages    Disadvantages   Examples                   __________________________________________________________________________     Surface                                                                              After the actuator is energized, it                                                            ♦ Fabrication simplicity                                                       ♦ Low                                                                            ♦                                                                Thermal inkjet             tension                                                                              typically returns rapidly to its normal                                                        ♦ Operational simplicity                                                       ♦ Surface tension force                                          relatively      ♦                                                                Piezoelectric inkjet             position. This rapid return sucks in                                                                          small compared to actuator                                                                    ♦                                                                IJ01-IJ07, IJ10-IJ14             air through the nozzle opening. The                                                                          ♦ Long refill time                                               usually dominates                                                                              ♦ IJ16,                                                          IJ20, IJ22-IJ45                  ink surface tension at the nozzle then                                                                        the total repetition rate                       exerts a small force restoring the                                             meniscus to a minimum area.                                              Shuttered                                                                            Ink to the nozzle chamber is                                                                   ♦ High speed                                                                   ♦ Requires common ink                                            pressure        ♦ IJ08,                                                          IJ13, IJ15, IJ17           oscillating                                                                          provided at a pressure that oscillates                                                         ♦ Low actuator energy, as                                                       oscillator     ♦ IJ18,                                                          IJ19, IJ21                 ink pressure                                                                         at twice the drop ejection frequency.                                                           actuator need only open or                                                                  ♦ May not be suitable                                            for pigmented                                    When a drop is to be ejected, the                                                               close the shutter, instead of                                                                inks                                            shutter is opened for 3 half cycles:                                                            ejecting the ink drop                                         drop ejection, actuator return, and                                            refill.                                                                  Refill                                                                               After the main actuator has ejected a                                                          ♦ High speed, as the nozzle                                                    ♦ Requires two                                                   independent     ♦ IJ09       actuator                                                                             drop a second (refill) actuator is                                                              actively refilled                                                                            actuators per nozzle                            energized. The refill actuator pushes                                          ink into the nozzle chamber. The                                               refill actuator returns slowly, to                                             prevent its return from emptying the                                           chamber again.                                                           Positive                                                                             The ink is held a slight positive                                                              ♦ High refill rate, therefore                                                  ♦ Surface spill must be                                          prevented       ♦                                                                Silverbrook, EP 0771       ink pressure                                                                         pressure. After the ink drop is                                                                 high drop repetition rate is                                                                ♦ Highly hydrophobic                                             print head       658 A2 and related              ejected, the nozzle chamber fills                                                               possible      surfaces are required                                                                          patent applications             quickly as surface tension and ink            ♦                                                                Alternative for:                 pressure both operate to refill the           ♦                                                                IJ01-IJ07, IJ10-IJ14             nozzle.                                       ♦ IJ16,                                                          IJ20,                      __________________________________________________________________________                                                         IJ22-IJ45             

    __________________________________________________________________________     METHOD OF RESTRICTING BACK-FLOW THROUGH INLET                                  Description           Advantages   Disadvantages    Examples                   __________________________________________________________________________     Long inlet                                                                           The ink inlet channel to the nozzle                                                            ♦ Design simplicity                                                           ♦ Restricts refill                                                                ♦                                                                Thermal inkjet             channel                                                                              chamber is made long and relatively                                                            ♦ Operational simplicity                                                      ♦ May result in a                                                relatively large ♦                                                                Piezoelectric inkjet             narrow, relying on viscous drag to                                                             ♦ Reduces crosstalk                                                            chip area       ♦ IJ42,                                                          IJ43                             reduce inlet back-flow.      ♦ Only partially                                                 effective                                   Positive                                                                             The ink is under a positive pressure,                                                          ♦ Drop selection and                                                          ♦ Requires a method                                              (such as a       ♦                                                                Silverbrook, EP 0771       ink pressure                                                                         so that in the quiescent state some of                                                          separation forces can be                                                                    nozzle rim or effective                                                                         658 A2 and related              the ink drop already protrudes from                                                             reduced      hydrophobizing, or both)                                                                        patent applications             the nozzle.     ♦ Fast refill time                                                             prevent flooding of the                                                                        ♦                                                                Possible operation               This reduces the pressure in the                                                                             surface of the print                                                                            of the following:               nozzle chamber which is required to           ♦                                                                IJ01-IJ07, IJ09-IJ12             eject a certain volume of ink. The            ♦ IJ14,                                                          IJ16, IJ20, IJ22,                reduction in chamber pressure results         ♦                                                                IJ23-IJ34, IJ36-IJ41             in a reduction in ink pushed out              ♦ IJ44             through the inlet.                                                       Baffle                                                                               One or more baffles are placed in the                                                          ♦ The refill rate is not                                                      ♦ Design                                                                          ♦ HP                                                             Thermal Ink Jet                  inlet ink flow. When the actuator is                                                            restricted as the long inlet                                                               ♦ May increase                                                   fabrication      ♦                                                                Tektronix                        energized, the rapid ink movement                                                               method.      complexity (e.g. Tektronix                                                                      piezoelectric ink                                                             jet                              creates eddies which restrict the flow                                                          ♦ Reduces crosstalk                                                           melt Piezoelectric print heads).                 through the inlet. The slower refill                                           process is unrestricted, and does not                                          result in eddies.                                                        Flexible flap                                                                        In this method recently discloed by                                                            ♦ Significantly reduces                                                       ♦ Not applicable to most                                         inkjet           ♦                                                                Canon                      restricts                                                                            Canon, the expanding actuator                                                                   flow for edge-shooter                                                                       configurations                             inlet (bubble) pushes on a flexible flap                                                              thermal ink jet devices                                                                    ♦ Increased fabrication                                          complexity                                        that restricts the inlet.    ♦ Inelastic deformation                                          of polymer                                                                      flap results in creep over extended                                            use                                        Inlet filter                                                                         A filter is located between the ink                                                            ♦ Additional advantage of                                                     ♦ Restricts refill                                                                ♦ IJ04,                                                          IJ12, IJ24, IJ27                 inlet and the nozzle chamber. The                                                               filtration  ♦ May result in complex                                          construction     ♦ IJ29,                                                          IJ30                             filter has a multitude of small holes                                                          ♦ Ink filter may be fabricated                   or slots, restricting ink flow. The                                                             with no additional process                                    filter also removes particles which                                                             steps                                                         may block the nozzle.                                                    Small inlet                                                                          The ink inlet channel to the nozzle                                                            ♦ Design simplicity                                                           ♦ Restricts refill                                                                ♦ IJ02,                                                          IJ37, IJ44                 compared to                                                                          chamber has a substantially smaller                                                                         ♦ May result in a                                                relatively large chip                       nozzle                                                                               cross section than that of the nozzle,                                                                       area                                             resulting in easier ink egress out of                                                                       ♦ Only partially                                                 effective                                         the nozzle than out of the inlet.                                        Inlet shutter                                                                        A secondary actuator controls the                                                              ♦ Increases speed of the                                                      ♦ Requires separate                                              refill actuator and                                                                             ♦ IJ09             position of a shutter, closing off the                                                          jet print head operation                                                                    drive circuit                                    ink inlet when the main actuator is                                            energized.                                                               The inlet is                                                                         The method avoids the problem of                                                               ♦ Back-flow problem                                                           ♦ Requires careful                                               design to minimize                                                                              ♦ IJ01,                                                          IJ03, IJ05, IJ06           located                                                                              inlet back-flow by arranging the ink-                                                           eliminated   the negative pressure behind                                                                   ♦ IJ07,                                                          IJ10, IJ11, IJ14           behind                                                                               pushing surface of the actuator                                                                              paddle          ♦ IJ16,                                                          IJ22, IJ23, IJ25           the ink-                                                                             between the inlet and the nozzle.             ♦ IJ28,                                                          IJ31, IJ32, IJ33           pushing                                             ♦ IJ34,                                                          IJ35, IJ36, IJ39           surface                                             ♦ IJ                                                             40, IJ41                   Part of the                                                                          The actuator and a wall of the ink                                                             ♦ Significant reductions                                                      ♦ Small increase in                                              fabrication      ♦ IJ07,                                                          IJ20, IJ26, IJ38           actuator                                                                             chamber are arranged so that the                                                                back-flow can be achieved                                                                   complexity                                 moves to                                                                             motion of the actuator closes off the                                                          ♦ Compact designs possible                 shut off the                                                                         inlet.                                                                   inlet                                                                          Nozzle                                                                               In some configurations of ink jet,                                                             ♦ Ink back-flow problem                                                       ♦ None related to ink                                            back-flow on     ♦                                                                Silverbrook, EP 0771       actuator does                                                                        there is no expansion or movement                                                               eliminated   actuation        658 A2 and related        not result in                                                                        of an actuator which may cause ink             patent applications       ink back-                                                                            back-flow through the inlet.                  ♦                                                                Valve-jet                  flow                                                ♦                                                                Tone-jet                                                                       ♦ IJ08,                                                          IJ13, IJ15, IJ17                                                               ♦ IJ18,                                                          IJ19,                      __________________________________________________________________________                                                         IJ21                  

    __________________________________________________________________________     NOZZLE CLEARING METHOD                                                         Description           Advantages    Disadvantages   Examples                   __________________________________________________________________________     Normal                                                                               All of the nozzles are fired                                                                   ♦ No added complexity on                                                       ♦ May not be sufficient                                          to displace     ♦ Most                                                           ink jet systems            nozzle                                                                               periodically, before the ink has a                                                              print head    ink            ♦                                                                IJ01-IJ07, IJ09-IJ12       firing                                                                               chance to dry. When not in use the            ♦ IJ14,                                                          IJ16, IJ20, IJ22                 nozzles are sealed (capped) against           ♦                                                                IJ23-IJ34, IJ36-IJ45             air.                                                                           The nozzle firing is usually                                                   performed during a special clearing                                            cycle, after first moving the print                                            head to a cleaning station.                                              Extra power                                                                          In systems which heat the ink, but do                                                          ♦ Can be highly effective                                                      ♦ Requires higher drive                                          voltage for     ♦                                                                Silverbrook, EP 0771       to ink heater                                                                        not boil it under normal situations,                                                            the heat is adjacent to the                                                                  clearing        658 A2 and related              nozzle clearing can be achieved by                                                              nozzle       ♦ May require larger                                             drive transistors                                                                               patent applications             over-powering the heater and boiling                                           ink at the nozzle.                                                       Rapid The actuator is fired in rapid                                                                 ♦ Does not require extra                                                       ♦ Effectiveness depends                                          substantially   ♦ May                                                            be used with:              succession                                                                           succession. In some configurations,                                                             circuits on the the print head                                                               upon the configuration of the                                                                 ♦                                                                IJ01-IJ07, IJ09-IJ11       of actuator                                                                          this may cause heat build-up at the                                                            ♦ Can be readily controlled                                                     nozzle         ♦ IJ14,                                                          IJ16, IJ20, IJ22           pulses                                                                               nozzle which boils the ink, clearing                                                            and initiated by digital logic                                                                              ♦                                                                IJ23-IJ25, IJ27-IJ34             the nozzle. In other situations, it may       ♦                                                                IJ36-IJ45                        cause sufficient vibrations to                                                 dislodge clogged nozzles.                                                Extra power                                                                          Where an actuator is not normally                                                              ♦ A simple solution                                                            ♦ Not suitable where                                             there is a hard ♦ May                                                            be used with:              to ink                                                                               driven to the limit of its motion,                                                              applicable    limit to actuator movement                                                                    ♦ IJ03,                                                          IJ09, IJ16, IJ20           pushing                                                                              nozzle clearing may be assisted by            ♦ IJ23,                                                          IJ24, IJ25, IJ27           actuator                                                                             providing an enhanced drive signal            ♦ IJ29,                                                          IJ30, IJ31, IJ32                 to the actuator.                              ♦ IJ39,                                                          IJ40, IJ41, IJ42                                                               ♦ IJ43,                                                          IJ44, IJ45                 Acoustic                                                                             An ultransonic wave is applied to the                                                          ♦ A high nozzle clearing                                                       ♦ High implementation                                            cost if         ♦ IJ08,                                                          IJ13, IJ15, IJ17           resonance                                                                            ink chamber. The wave is of an                                                                  capability can be achieved                                                                   system does not already include                                                               ♦ IJ18,                                                          IJ19, IJ21                       appropriate amplitude and frequency                                                            ♦ May be implemented                                                            acoustic actuator                               to cause sufficient force at the nozzle                                                         very low cost in systems                                      to clear blockages. This is easiest to                                                          which already include                                         achieve if the ultrasonic wave is at a                                                          acoustic actuators                                            resonant frequency of the ink cavity.                                    Nozzle                                                                               A microfabricated plate is pushed                                                              ♦ Can clear severely                                                           ♦ Accurate mechanical                                            alignment is    ♦                                                                Silverbrook, EP 0771       clearing                                                                             against the nozzles. The plate has a                                                            nozzles       required        658 A2 and related        plate post for every nozzle. The array of                                                                          ♦ Moving parts are                                               required         patent applications             posts                         ♦ There is risk of                                               damage to the                                                                   nozzles                                                                       ♦ Accurate fabrication                                           is required                                Ink pressure                                                                         The pressure of the ink is                                                                     ♦ May be effective where                                                       ♦ Requries pressure                                              pump or other   ♦ May                                                            be used with all           pulse temporarily increased so that ink                                                               other methods cannot be                                                                      pressure actuator                                                                              IJ series ink jets              streams from all of the nozzles. This                                                           used         ♦ Expensive                        may be used in conjunction with                                                                              ♦ Wasteful of ink                  actuator energizing.                                                     Print head                                                                           A flexible `blade` is wiped across the                                                         ♦ Effective for planar                                                         ♦ Difficult to use if                                            print head      ♦ Many                                                           ink jet systems            wiper print head surface. The blade is                                                                head surfaces                                                                                surface is non-planar or very                   usually fabricated from a flexible                                                             ♦ Low cost                                                                      fragile                                         polymer, e.g. rubber or synthetic                                                                            ♦ Requires mechanical                                            parts                                            elastomer.                    ♦ Blade can wear out in                                          high volume                                                                     print systems                             Separate ink                                                                         A separate heater is provided at the                                                           ♦ Can be effective where                                                       ♦ Fabrication                                                    complexity      ♦ Can                                                            be used with               boiling                                                                              nozzle although the normal drop e-                                                              other nozzle clearing         many IJ series ink        heater                                                                               ection mechanism does not require it.                                                           methods cannot be used        jets                            The heaters do not require individual                                                          ♦ Can be implemetned at no                       drive circuits, as many nozzles can                                                             additional cost in some                                       be cleared simultaneously, and no                                                               inkjet configurations                                         imaging is required.                                                     __________________________________________________________________________

    __________________________________________________________________________     NOZZLE PLATE CONSTRUCTION                                                      Description           Advantages    Disadvantages   Examples                   __________________________________________________________________________     Electro-                                                                             A nozzle plate is separately                                                                   ♦ Fabrication simplicity                                                       ♦ High temperature and                                           pressures are   ♦                                                                Hewlett Packard            formed                                                                               fabricated from electroformed nickel,                                                                         required to bond nozzle plate             nickel                                                                               and bonded to the print head chip.                                                                           ♦ Minimum thickness                                              constraints                                                                    ♦ Differential thermal                                           expansion                                  Laser ablated                                                                        Individual nozzle holes are ablated                                                            ♦ No masks required                                                            ♦ Each hole must be                                              individually    ♦ Canon                                                          Bubblejet                  or drilled                                                                           by an intense UV laser in a nozzle                                                             ♦ Can be quite fast                                                             formed         ♦ 1988                                                           Sercel et al.,             polymer                                                                              plate, which is typically a polymer                                                            ♦ Some control over                                                            ♦ Special equipment                                              required         SPIE, Vol. 998                  such as polyimide or polysulphone                                                               profile is possible                                                                         ♦ Slow where there are                                           many             Excimer Beam                                    ♦ Equipment required                                                            thousands of nozzles per print                                                                 Applications, pp.                                                             76-                                               relatively low cost                                                                         ♦ May produce thin                                               burrs at exit    83                                                             holes          ♦ 1993                                                           Watanabe et al.                                                                 U.S. Pat No.                                                                   5,208,6043                Silicon                                                                              A separate nozzle plate is                                                                     ♦ High accuracy is attainable                                                  ♦ Two part                                                                       ♦ K.                                                             Bean, IEEE                 micro-                                                                               micromachined from single crystal                                                                            ♦ High                                                                            Transactions on           machined                                                                             silicon, and bonded to the print head                                                                        ♦ Requires precision                                             alignment        Electron Devices,               wafer.                        ♦ Nozzles may be                                                 clogged by       Vol. ED-25, No. 10,                                            adhesive        1978, pp 1185-1195                                                            ♦ Xerox                                                          1990 Hawkins                                                                    et al., U.S. Pat.                                                             No.                                                                             4,899,181                 Glass Fine glass capillaries are drawn from                                                          ♦ No expensive equipment                                                       ♦ Very small nozzle                                              sizes are       ♦ 1970                                                           Zoltan U.S.                capillaries                                                                          glass tubing. This method has been                                                              required      difficult to form                                                                              Pat. No. 3,683,212              used for making individual nozzles,                                                            ♦ Simple to make single                                                        ♦ Not suited for mass                                            production                                       but is difficult to use for bulk                                                                nozzles                                                       manufacturing of print heads with                                              thousands of nozzles.                                                    Monolithic,                                                                          The nozzle plate is deposited as a                                                             ♦ High accuracy (<1                                                            ♦ Requires sacrificial                                           layer under the ♦                                                                Silverbrook, EP 0771       surface                                                                              layer using standard VLSI deposition                                                           ♦ Monolithic                                                                    nozzle plate to form the                                                                       658 A2 and related        micro-                                                                               techniques. Nozzles are etched in the                                                          ♦ Low cost                                                                      chamber         patent applications       machined                                                                             nozzles plate using VLSI lithography                                                           ♦ Existing processes can                                                       ♦ Surface may be                                                 fragile to the touch                                                                           ♦ IJ01,                                                          IJ02, IJ04, IJ11           using VLSI                                                                           and etching.     used                         ♦ IJ12,                                                          IJ17, IJ18, IJ20           lithographic                                        ♦ IJ22,                                                          IJ24, IJ27, IJ28           processes                                           ♦ IJ29,                                                          IJ30, IJ31, IJ32                                                               ♦ IJ33,                                                          IJ34, IJ36, IJ37                                                               ♦ IJ38,                                                          IJ39, IJ40, IJ41                                                               ♦ IJ42,                                                          IJ43, IJ44                 Monolithic,                                                                          The nozzle plate is a buried etch stop                                                         ♦ High accuracy (<1                                                            ♦ Requires long etch                                             times           ♦ IJ03,                                                          IJ05, IJ06, IJ07           etched                                                                               in the wafer. Nozzle chambers are                                                              ♦ Monolithic                                                                   ♦ Requires a support                                             wafer           ♦ IJ08,                                                          IJ09, IJ10, IJ13           through                                                                              etched in the front of the wafer, and                                                          ♦ Low cost      ♦ IJ14,                                                          IJ15, IJ16, IJ19           substrate                                                                            the wafer is thinned from the back                                                             ♦ No differential expansion                                                                    ♦ IJ21,                                                          IJ23, IJ25, IJ26                 sie. Nozzles are then etched in the                                            etch stop layer.                                                         No nozzle                                                                            Various methods have been tried to                                                             ♦ No nozzles to become                                                         ♦ Difficult to control                                           drop position   ♦ Ricoh                                                          1995 Sekiya et             plate eliminate the nozzles entirely, to                                                              clogged       accurately      al U.S. Pat No.                 prevent nozzle clogging. These                                                                               ♦ Crosstalk                                                                       5,412,413                       include thermal bubble mechanisms             ♦ 1993                                                           Hadimioglu et                    and acoustic lens mechanisms                   al EUP 550,192                                                                ♦ 1993                                                           Elrod et al EUP                                                                 572,220                   Trough                                                                               Each drop ejector has a trough                                                                 ♦ Reduced manufacturing                                                        ♦ Drop firing direction                                          is sensitive to ♦ IJ35             through which a paddle moves.                                                                   complexity    wicking.                                        There is no nozzle plate.                                                                      ♦ Monolithic                               Nozzle slit                                                                          The elimination of nozzle holes and                                                            ♦ No nozzles to become                                                         ♦ Difficult to control                                           drop position   ♦ 1989                                                           Saito et al                instead of                                                                           replacement by a slit encompassing                                                              clogged       accurately      U.S. Pat. No.             individual                                                                           many actuator positions reduces                                                                              ♦ Crosstalk                                                                       4,799,068                 nozzles                                                                              nozzle clogging, but increases                                                                               ♦ Crosstalk problems               crosstalk due to ink surface waves                                       __________________________________________________________________________

    __________________________________________________________________________     DROP EJECTION DIRECTION                                                        Description           Advantages    Disadvantages   Examples                   __________________________________________________________________________     Edge  Ink flow is along the surface of the                                                           ♦ Simple construction                                                          ♦ Nozzles limited to                                             edge            ♦ Canon                                                          Bubblejet                  (`edge                                                                               chip, and ink drops are ejected from                                                           ♦ No silicon etching                                                           ♦ High resolution is                                             difficult        1979 Endo et al GB        shooter`)                                                                            the chip edge.  ♦ Good heat sinking                                                            ♦ Fast color printing                                            requires one     patent 2,007,162                                 substrate     print head per color                                                                          ♦ Xerox                                                          heater-in-pit                                    ♦ Mechanically strong                                                                           1990 Hawkins et al                              ♦ Ease of chip handing                                                                          U.S. Pat. No.                                                                  4,899,181                                                                     ♦                                                                Tone-jet                   Surface                                                                              Ink flow is along the surface of the                                                           ♦ No bulk silicon etching                                                      ♦ Maximum ink flow is                                            severely        ♦                                                                Hewlett-Packard TIJ        (`roof                                                                               chip, and ink drops are ejected from                                                            required      restricted      1982 Vaught et al         shooter`)                                                                            the chip surface, normal to the plane                                                          ♦ Silicon can make an                                                                           U.S. Pat No.                    of the chip.     effective heat sink           4,490,728                                       ♦ Mechanical strength                                                                          ♦ IJ02,                                                          IJ11, IJ12, IJ20                                                               ♦ IJ22       Through                                                                              Ink flow is through the chip, and ink                                                          ♦ High ink flow                                                                ♦ Requires bulk silicon                                          etching         ♦                                                                Silverbrook, EP 0771       chip, drops are ejected from the front                                                               ♦ Suitable for pagewidth                                                                        658 A2 and related        forward                                                                              surface of the chip.                                                                           ♦ High nozzle packing                                                                           patent applications       (`up                   density therefore low        ♦ IJ04,                                                          IJ17, IJ18, IJ24           shooter`)              manufacturing cost           ♦                                                                IJ27-IJ45                  Through                                                                              Ink flow is through the chip, and ink                                                          ♦ High ink flow                                                                ♦ Requries wafer                                                 thinning        ♦ IJ01,                                                          IJ03, IJ05, IJ06           chip, drops are ejected from the rear                                                                ♦ Suitable for pagewidth                                                       ♦ Requires special                                               handling during ♦ IJ07,                                                          IJ08, IJ09, IJ10           reverse                                                                              surface of the chip.                                                                           ♦ High nozzle packing                                                           manufacture    ♦ IJ13,                                                          IJ14, IJ15, IJ16           (`down                 density therefore low        ♦ IJ19,                                                          IJ21, IJ23, IJ25           shooter`)              manufacturing cost           ♦ IJ26       Through                                                                              Ink flow is through the actuator,                                                              ♦ Suitable for piezoelectric                                                   ♦ Pagewidth print heads                                          require         ♦ Epson                                                          Stylus                     actuator                                                                             which is not fabricated as part of the                                                          print heads   several thousand connections                                                                  ♦                                                                Tektronix hot melt               same substrate as the drive    drive circuits  piezoelectric ink                                                             jets                             transistors.                  ♦ Cannot be                                                      manufactured in                                                                 standard CMOS fabs                                                            ♦ Complex assembly                                               required                                   __________________________________________________________________________

    __________________________________________________________________________     INK TYPE                                                                       Description           Advantages    Disadvantages   Examples                   __________________________________________________________________________     Aqueous,                                                                             Water based ink which typically                                                                ♦ Environmentally friendly                                                     ♦ Slow                                                                           ♦ Most                                                           existing inkjets           dye   contains: water, dye, surfactant,                                                              ♦ No odor                                                                      ♦ Corrosive                                                                      ♦ All                                                            IJ series ink jets               humectant, and biocide.       ♦ Bleeds on                                                                      ♦                                                                Silverbrook, EP 0771             Modern ink dyes have high water-                                                                             ♦ May                                                                             658 A2 and related              fastness, light fastness      ♦ Cockles                                                                         patent applications       Aqueous,                                                                             Water based ink which typically                                                                ♦ Environmentally friendly                                                     ♦ Slow                                                                           ♦ IJ02,                                                          IJ04, IJ21, IJ26           pigment                                                                              contains: water, pigment, surfactant,                                                          ♦ No odor                                                                      ♦ Corrosive                                                                      ♦ IJ27,                                                          IJ30                             humectant, and biocide.                                                                        ♦ Reduced bleed                                                                ♦ Pigment may clog                                               nozzles         ♦                                                                Silverbrook EP 0771              Pigments have an advantage in                                                                  ♦ Reduced wicking                                                              ♦ Pigment may clog                                               actuator         658 A2 and related              reduced bleed, wicking and                                                                     ♦ Reduced strikethrough                                                         mechanisms      patent applications             strikethrough.                ♦ Cockles                                                                        ♦                                                                Piezoelectric                                                                  ink-jets                                                                       ♦                                                                Thermal ink jets                                                                (with significant                                                              restrictions)             Methyl Ethyl                                                                         MEK is a highly volatile solvent                                                               ♦ Very fast drying                                                             ♦ Odorous                                                                        ♦ All                                                            IJ series ink jets         Ketone                                                                               used for industrial printing on                                                                ♦ Prints on various                                                            ♦ Flammable                  (MEK) difficult surfaces such as aluminum                                                             such as metals and plastics                                   cans.                                                                    Alcohol                                                                              Alcohol based inks can be used                                                                 ♦ Fast drying                                                                  ♦ Slight                                                                         ♦ All                                                            IJ series ink jets         (ethanol, 2-                                                                         where the printer must operate at                                                              ♦ Operates at sub-freezing                                                     ♦ Flammable                  butanol, and                                                                         temperatures below the freezing                                                                 temperatures                                            others)                                                                              point of water. An example of this is                                                          ♦ Reduced paper cockle                           in-camera consumer photographic                                                                ♦ Low cost                                       printing.                                                                Phase The ink is solid at room temperature.                                                          ♦ No drying time- ink                                                          ♦ High                                                                           ♦                                                                Tektronix hot melt         change                                                                               and is melted in the print head before                                                          instantly freezes on the                                                                    ♦ Printed ink typically                                          has a `waxy`     piezoelectric ink                                                             jets                       (hot melt)                                                                           jetting. Hot melt inks are usually                                                              print medium  feel           ♦ 1989                                                           Nowak U.S.                       wax based, with a melting piont                                                                ♦ Almost any print medium                                                      ♦ Printed pages may                                              `block`          Pat. No. 4,820,346              around 80° C. After jetting the ink                                                      can be used  ♦ Ink temperature may                                            be above the    ♦ All                                                            IJ series ink jets               freezes almost instantly upon                                                                  ♦ No paper cockle occurs                                                        curie point of permanent magnets                contacting the print medium or a                                                               ♦ No wicking occurs                                                            ♦ Ink heaters consume                                            power                                            transfer roller.                                                                               ♦ No bleed occurs                                                              ♦ Long warm-up time                                ♦ No strikethrough occurs                  Oil   Oil based inks are extensively used                                                            ♦ High solubility medium                                                       ♦ High viscosity: this                                           is a signficant ♦ All                                                            IJ series ink jets               in offset printing. They have                                                                   some dyes     limitation for use in inkjets,                  advantages in improved                                                                         ♦ Does not cockle paper                                                         which usually require a low                     characteristics on paper (especially                                                           ♦ Does not wick through                                                         viscosity. Some short chain and                 no wicking or cockle). Oil soluble                                                              paper         multi-branched oils have a                      dies and pigments are required.                                                                               sufficiently low viscosity.                                                   ♦ Slow drying                Micro-                                                                               A microemulsion is a stable, self                                                              ♦ Stops ink bleed                                                              ♦ Viscosity higher than                                          water           ♦ All                                                            IJ series ink jets         emulsion                                                                             forming emulsion of oil, water, and                                                            ♦ High dye solubility                                                          ♦ Cost is slightly                                               higher than water                                surfactant. The characteristic drop                                                            ♦ Water, oil, and amphiphilic                                                   based ink                                       size is less than 100 nm, and is                                                                soluble dies can be used                                                                    ♦ High surfactant                                                concentration                                    determined by the preferred                                                                    ♦ Can stabilize pigment                                                         required (around 5%)                            curvature of the surfactant.                                                                    suspensions                                             __________________________________________________________________________ 

We claim:
 1. A method of brushing a simulated brush stroke along a path in a computer graphics image said method comprising the steps of:converting the path to a series of corresponding line segments; determining a current convex brush edge of said path; determining a series of substantially equally spaced points along said convex edge; determining corresponding parametric points along said path; and utilising said parametric points to place brush template structures in said computer graphics image.
 2. A method as claimed in claim 1 wherein said brush template structures includes an opacity channel which is combined with the opacity channel of the computer graphic image.
 3. A method as claimed in claim 2 wherein said opacity channel is combined such that the maximum of a current brush template opacity value and a current computer graphic image opacity channel value becomes the new current computer graphic image opacity channel value.
 4. A method as claimed in claim 2 wherein said opacity channel is combined such that the minimum of a current brush template opacity value and a current computer graphic image opacity channel value becomes the new current computer graphic image opacity channel value.
 5. A method as claimed in claim 2 wherein said computer graphic image further comprises a footprint channel which is set when each pixel is composited and said opacity channel is only composited with the computer graphic image opacity channel when said footprint channel is not set.
 6. A method as claimed in claim 1 wherein said computer graphic image comprises a brushing buffer which is subsequently combined with a second computer graphic image so as to form a final computer graphics image. 